﻿<p>An <em>IfcSurfaceCurve</em> is a 3-dimensional curve that has additional representations provided by one or two pcurves.</p>

<blockquote class="extDef">
NOTE&nbsp; Definition according to ISO/CD 10303-42:1992<br>
A surface curve is a type of curve, that is a curve on a surface. The curve is represented as a curve (curve_3d) in three-dimensional space and possibly as a curve, corresponding to a pcurve, in the two-dimensional parametric space of a surface. The ability of this curve to reference a list of 1 or 2 pcurves enables this entity to define either a curve on a single surface, or an intersection curve which has two distinct surface associations. A `seam' on a closed surface can also be represented by this entity; in this case each associated_geometry will be a pcurve lying on the same surface. Each pcurve shall be parametrised to have the same sense as curve_3d. The surface curve takes its parametrisation directly from either curve_3d or pcurve as indicated by the attribute master representation. </blockquote> 

<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>surface_curve</strong> defined in ISO 10303-42.</blockquote>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC4 Add2.
</blockquote>

<p class="spec-head">Informal Propositions:</p> 
<ol> 
<li>Where <em>Curve3D</em> and one or two pcurves exist they shall represent the same mathematical point set. (i.e., they shall coincide geometrically but may differ in parametrisation.)</li> 
<li>The <em>Curve3D</em> and any associated pcurves shall agree with respect to their senses.</li> 
</ol> 